Aluminum is a high value-added rare metal having excellent conductivity, corrosion resistance, and workability, and thus, it is used as alloy or a secondary material of special steel through the combination with various elements. As a result, there is a high demand for aluminum as a raw material.
In view of the fact that 97% of the total amount of resources consumed in Korea is dependent upon imports, especially, importing the aluminum raw material causes enormous financial damages, and therefore, aluminum recycling industry has been the center of interest, so that the waste aluminum raw material is grinded to fine particles and thus recycled to aluminum granules having high purity.
One of grinding apparatuses is disclosed in Korean Patent Application No. 10-2013-0110039 (entitled: aluminum granule recycling process) filed by the same applicant as the invention, wherein a high speed grinding apparatus adequate to aluminum grinding includes rotary blades located in multiple stages, a fixed blade part located outside the rotary blades and having vortex flow grooves formed to generate vortex flows therefrom, and an impeller adapted to increase the discharge pressure of air, thereby activating the particle collision through the rotation of the rotary blades and the vortex flows generated by the vortex flow grooves of the fixed blade part thus to manufacture the granules having particle sizes in the range between 100 μm and 1000 μm.
The high speed grinding apparatus as mentioned above performs the particle collision of the grinded object just through the rotation of the rotary blades and the vortex flows generated by the vortex flow grooves of the fixed blade part, thereby allowing the grinded object to be grinded to the particle sizes in the range between 200 μm and 2000 μm, but failing to grind them to the particle sizes less than 200 μm.
Generally, a jet mill includes producing means for generating high pressure air, a body connected to the producing means and having a grinding chamber formed at the interior thereof, and injection nozzles spaced apart from each other along the body to inject the high pressure air moved from the producing means into the grinding chamber of the body and thus to generate swirling movements.
In case of such jet mills, however, the injection nozzles are located protrudedly from the body toward the inside of the grinding chamber, so that the protruded portions of the injection nozzles are easily abraded during the grinding of waste aluminum due to a high degree of softness of aluminum, which inconveniently causes frequent exchange of the injection nozzles.
Generally, aluminum generates excessive heat upon particle collision and is easily melted by heat due to a high degree of softness, and so as to grind waste aluminum, thus, the same time-particle collision should be maximized and the heat generated during grinding should be effectively distributed and dissipated. In case where the jet mill is applied to the grinding of waste aluminum, accordingly, it has to be precisely designed to optimize the number of injection nozzles and the installation angles of the injection nozzles and thus to maximize the particle collision. However, the conventional jet mill is not designed in consideration of the properties of aluminum, and therefore, it is not adequate for aluminum grinding.
Accordingly, many studies should be definitely needed on the jet mill capable of grinding waste aluminum raw materials to particle sizes of 1000 μm.
FIG. 1 is a plan sectional view showing one example of conventional jet mills, which is disclosed in Korean Patent No. 10-0673976 (entitled ‘swirling flow type jet mill’).
A jet mill 900 (hereinafter referred to as conventional jet mill) as shown in FIG. 1 includes a grinding chamber 901, supply nozzles 903 and auxiliary nozzles 904 adapted to inject air into the grinding chamber 901, a discharge hole 905 formed at the center of the grinding chamber 901 to discharge fine particles therefrom, and spiral wings 907 equally spaced apart from each other on the concentric circle around the discharge hole 905.
The supply nozzles 903 and the auxiliary nozzles 904 are spaced apart from each other along the inner periphery of the grinding chamber 901 in such a manner as to have their injection direction located against the center of the grinding chamber 901, thereby forming the swirling flows of air in the interior of the grinding chamber 901 through the injection of air.
Further, each spiral wing 907 is reduced in radius from the center of the discharge hole 905 as it goes from the upper flow side end 907a to the lower flow side end 907b, so that the grinded object collide against each other by means of the spiral wings 907, thereby increasing the grinding efficiency.
According to the conventional jet mill 900, however, the high expensive supply nozzles 903 and auxiliary nozzles 904 are mounted along the outer peripheral side wall 909 forming the grinding chamber 901, which makes the manufacturing complicated and further increases the manufacturing cost.
According to the conventional jet mill 900, further, the nozzle holes of the supply nozzles 903 and the auxiliary nozzles 904 are not located toward the discharge hole 905 as the center of the grinding chamber 901, but just located against the discharge hole 905, so that no structure is made wherein the number of nozzles and the approach angles of air are optimized to maximize the generation of turbulent flows, thereby failing to improve the number of injection nozzles—the turbulent flow efficiency and also failing to grind the grinded object into the fine granules having particle sizes less than 1000 μm.
So as to manufacture the aluminum granules having the particle sizes less than 1000 μm, that is, the approach angles toward air of the nozzles 903 and 904 and the number of them should be optimized to generate active turbulent flows in the grinding chamber 901, but the conventional jet mill 900 does not suggest any technology on the above, thereby failing to induce maximum particle collision.
According to the conventional jet mill 900, furthermore, the grinded object introduced should have the particle sizes in the range between 20 mm and 30 mm so as to induce the collision of the grinded object introduced through the pressuring air, and therefore, before the grinding process is performed using the jet mill 900, a pre-treatment process (grinding) should be performed wherein the grinded object is grinded to the particle sizes in the range between 20 mm and 30 mm. In the conventional grinding procedure using the jet mill 900, accordingly, the pre-treatment process, wherein the grinded object is grinded to the particle sizes in the range between 20 mm and 30 mm, and the grinding process using the jet mill 900, wherein the grinded object having the particle sizes in the range between 20 mm and 30 mm grinded through the pre-treatment process is grinded to fine particle sizes, should be performed independently of each other, thereby making the manufacturing procedure complicated and further causing the manufacturing time to be delayed.
Accordingly, many methods and devices are proposed to grind the grinded object having the particle sizes more than 30 mm to the fine particle sizes less than 1000 μm, not by using the jet mill, but by using the well-known grinding apparatus (fixed blades and rotary blades) adopted in the pre-treatment process (grinding), but when the grinded object becomes waste aluminum having a high degree of softness, low melting point and excessive heat generated during particle collision, the particle collision of the grinded object cannot be optimized by using the well-known grinding apparatus grinding the grinded object by the particle collision of the grinded object through the fixed blades and the rotary blades. Accordingly, there is an urgent need for the development and study on a new grinding apparatus capable of grinding waste aluminum into the fine granules having the particle sizes less than 1000 μm, not by using both of the pre-treatment process and the conventional jet mill.
That is, there is a definite demand for the development and study on a new grinding apparatus capable of grinding waste aluminum having the particle sizes more than 30 mm into the fine granules having the particle sizes in the range between 100 μm and 1000 μm and further effectively distributing and dissipating the heat generated during the grinding in consideration of the properties of the aluminum.